Effect of substitution of Mn by Cr on the 55Mn NMR and magnetoresistance in La0.6Sr0.2Mn1.2-xCrxO3 (0≤x≤0.2)

The La0.6Sr0.2Mn1.2-xCrxO3 (0≤x≤0.2) ceramic samples with perovskite-like structure (R 3-bar c) have been studied using the X-ray diffraction, NMR, magnetic and resistance methods. The 55Mn NMR spectrum was shown to depend strongly on the Cr/Mn ratio. A single symmetric line centered at 379 MHz was found for La0.6Sr0.2Mn1.2O3 (x=0). For La0.6Sr0.2Mn1.1Cr0.1O3, the 55Mn NMR spectrum is slightly expanded and shifted to lower frequencies. An analysis of the 55Mn NMR spectrum for the La0.6Sr0.2MnCr0.2O3 compound has shown that a wide asymmetrical line can be uniquely expanded into four components with different resonance frequencies. These components arise due to both different ionization states of the manganese ions and a non-equivalence of their crystallographic surrounding. There are manganese ions, whose ionization states are close to (3+) and (4+), as well as Mn ions with intermediate valence which resulted from the high-frequency electron exchange. The Curie temperature and the temperatures of both resistance maximum and magnetoresistance peak were found to decrease, while the value of magnetoresistance increases with increasing Cr content